The required bandwidth of a television signal is a function of the spatial (horizontal, vertical) and temporal resolution to be contained in the signal. As increased resolution is desired in either the vertical, horizontal or temporal directions the bandwidth of the signal must be increased. HDTV signals contain considerably more resolution than, for example, NTSC encoded signals. They therefore require significantly more bandwidth than the 9.5 MHz video bandwidth allowed per channel of satellite transmission. It is thus necessary to employ bandwidth reduction techniques in order to reduce the original bandwidth of an HDTV signal to transmission.
In the N.H.K. developed MUSE system, a lower bandwidth is achieved by trading off spatial resolution for temporal resolution. Other systems utilizing spatial-temporal exchange include the system described in the article "HDTV Colorimetry" by W. E. Glenn and K. G. Glenn, High Definition Television 1985 Colloquium Proceedings, and the system proposed in U.S. Pat. No. 4,694,338 of Mikhail Tsinberg, assigned to the same assignee as the present invention and incorporated by reference herein.
The exact means by which this trade-off is accomplished varies among these systems and is not restricted to only these methods. However all spatial-temporal exchange techniques result in some type of motion artifacts. One example of such artifacts is smear or seemingly further reduced spatial resolution when there is motion in the display.
Studies by B. Wendland, e.g. "High Definition Studies on a Compatible Basis with Present Standards" Television Technology in the 80's, Scarsdale, NY, SMPTE, 1981, pp. 151-165 have shown that the two dimensional spatial response of the human visual system is not circular but somewhat diamond shaped. It is therefore concluded that the visual system has more capability to resolve truly horizontal and vertical frequencies rather than diagonal frequencies.